I read somewhere (can't remember where) that preschool children can be taught and gain a lot of knowledge in specific areas and that this knowlege easily disappears a couple of years down the road when the focus has been shifted to something else. The examples were mostly in the domain of history and science.
I actually would not be overly concerned with the math facts as those should improve with normal practice unless your DD has a processing or memory issue. It is more disheartening that she lost almost two years of math concepts, especailly at the early elementary levels where the concepts tend to be intuitive. I would have her work in EPGY from her current level and you may be reassured when you see how quickly she leaps past the second and third grade work.
The only time that I have witnessed a noticeable drop in math ablity was in a child with mild autistic symptoms who displayed almost savant type math abilities at a young age and those abilities disappeared when the autistic symptoms improved substantially.
